Method of casting



NOV. 3, 1942. w NQ 2,301,027

METHOD OF CASTING Filed July 2, 1958 5 Sheets-Sheet 1 eldon Nov. 3,1942. w. T. ENNOR 2,301,027

METHOD OF CASTING Filed July 2, 1938 5 Sheets-Sheet 2 Nov. 3, 1942. w.T. ENNOR 2,301,027

METHOD OF CASTING Filed July 2, 1938 5 Sheets-Sheet 3 NOV. 3, 1942. w,ENNQR 2,301,027

METHOD OF CASTING Filed July 2, 1958 5 Sheets-Sheet 4 inventor 1: Emwr,

By Win-1 (Ittorneg Patented Nov. 3, 1942 METHOD OF CASTING William T.Ennor, Massena, N. Y., assignor to Aluminum Company of America,Pittsburgh, Pa., a corporation of Pennsylvania Application July 2, 1938,Serial No. 217,200

14 Claims.

This invention relates to the casting of ingots of light metals andalloys thereof, by which latter terms I mean aluminum and its alloys andmagnesium and its alloys. The invention is particularly adapted to theproduction of ingots of large cross section and indeterminate length.

Particularly, in the production of large structural shapes and forgingsof aluminum and its alloys, larger and larger ingot has been required.Larger ingots of magnesium and its alloys are also desirable. Ingotcasting methods which had proved satisfactory in the production ofingots oi the smaller cross sections were tried out in the production ofthe new sizes called for today, but the results were not at allsatisfactory. The larger ingot was unsound or the structure of the metalso inferior as to lead to difliculties in subsequent working. Among thedifliculties encountered, the cracking of the ingot during working andthe unsatisfactory final heat-treated properties of the metal were foundto be particularly serious. These and other considerations appear todepend upon the structural characteristics of the metal as cast.

I have observed that the working characteristics of light metal ingotare determined largely by the size and distribution of the undissolvedalloying constituent. If-the undissolved constituent is coarse, i. e.present in the form of relatively large isolated particles, andtherefore less uniformly distributed than is to be desired, the workingcharacteristics are far less satisfactory than where there is a finerand more uniform distribution. 7

The detrimental effects of a coarse constituent distribution show up intwo different ways in light metal fabrication. First, coarse and unevendistribution of the constituent frequently results in cracking of theingot at some stage during the working of the metal. One manifestationof this is the cracking of the surfaces, edges or corners of the ingotduring the initial break-down stages. Again, cracking may occur at thecenter of the ingot. A particular difficulty which has been encounteredis the cracking that occurs during the later stages of fabrication undersevere conditions of stress. Examples of this which maybe mentioned are:the cracking encountered in rolling large structural shapes which in thecase of some channel sections shows up along the flanges; the crackingof the edges of plates and slabs; and that which occurs around theperiphery of metal being upset under a forging hammer.

The second manner in which a coarse constitu ent network can beinjurious is its effect in producing unsatisfactory properties in thefinal heat-treated product of these working operations.. In extremelylarge products, this may be true regardless of the direction in which atest sample is taken. For example, the mechanical properties of largeround or square sections after heat-treatment may be unsatisfactory evenin the direction of rollingi. e. longitudinally. As

10 the amount of working is increased, the constituent network tends tobe broken up and the properties improved. This improvement is quitenoticeable in the longitudinal direction, but in the transversedirection the harmful effect of the coarse constituent network persistseven after a very extensive working of the metal.

A better understanding of the nature of the problem presented, andtherefore of the objects of this invention which concern its solution,can

be gained from a consideration of the methods starting with; ingot oflarger size. This has failed to provide the solution. When casting theingot by known methods, it was found-that the increase in ingot sizeresults in an increase in coarseness of the constituent network, and

:llLthat this largely nullifies the beneficial effect of the increasedamount of hot working. Also, in breaking down the larger ingot with itscoarser constituent network, fracturing of the central regions of theingot becomes a more frequent and serious occurrence.

It has been known heretofore that in casting light metal ingot of verylarge cross section the manner of cooling the ingot influences thetendency' to form dendritic grain structures, and the .10 freedom fromthe defects of segregation, liquation and porosity. The best practiceprior to the time of the present invention is described in the Stay andHolzhauer Patents Nos. 1,777,657 and 1,777,658, granted October 7, 1930.According to 4:, the method of these paients, the metal in the mold isprogressivelyand gradually solidified from the bottom to the top of themold. This method is quite satisfactory in producing ingot for manypurposes but does not produce ingot .30 having a suiiiciently fine andeven distribution of the undissolved alloying constituent to avoidaltogether the various types of fabrication difiiculties which have beendescribed, or to make possible the attainment of satisfactory mechanicalproperties in heat-treated articles of the large sizes now demanded bythe light metal market.

With reference to the casting? of ingot in general, attempts have beenmade to fe d t e m al into a mold continuously whiletwithdrawing thepartially cooled metal down through th bottom of the mold and applying aliquid coolant to the surface of the metal below the mold. These methodswere not adapted to the casting of light metal ingot of large crosssection, principally because the cooling was not performed in a mannerto produce in such ingot a metal structure having a sufliciently fineand even distribution of the undissolved alloying constituent.

It is an object of the present invention to provide a method of castingaluminum ingot of large cross section which will possess improvedworking characteristics and make possible the attainment of improvedmechanical properties in large wrought and heat-treated articles madetherefrom.

More particularly, it is an object of my invention to provide a methodof casting light metal ingot which will not be subject to the varioustypes of cracking described hereinabove as occurring during break-downor later working stages.

A general object is to provide an ingot casting method by which soundlight metal ingot may be produced, which ingot is particularlycharacterized by the fineness and evenness of distribution of itsalloying constituent, with especial ref erence to the network of theundissolved constituent. A pictorial representation of this object isgiven in Figs. 6 and 8 of the drawings,

later to be described; it being an.object of my invention to provide aningot casting method by which there can be produced an aluminum ingot(of the alloy represented) which, as to fineness and evenness ofdistribution of the undissolved constituent, will approximate themicrostructure of this representation.

A further object is to provide a method by which production of largelight metal alloy ingot of the stated characteristics may b carried oneconomically and by which ingot of any desired length may be produced.

A further object is to provide apparatus for carrying out the novelmethod, including a novel form of mold and metal feeding means by whichthe novel steps of the method are performed.

A specific object is to provide a method of abstracting heat from metalcast to form an ingot whereby initially the heat may be withdrawnprincipally by absorption of radiant energy without metal-to-moldcontact.

Other objects and advantages will appear as the description proceeds.

The drawings illustrate an embodiment of the apparatus for carrying outthe method, the microstructure of the aluminum alloy ingot produced, anda graphical representation of essential steps of the general method.

Apparatus.Fig. 1 is a side elevation, partly in section, showing ageneral arrangement of apparatus suitable for carrying out the method.Fig. 2 is an elevational view on the line II-II of Fig. 1 showing aportion of the same apparatus. Fig. 3 is a vertical sectional view, toan enlarged scale, of the mold, ingot platform and metal-feedingarrangement of Figs. 1 and 2; the parts being shown in the positionoccupied at an intermediate point in the casting operation. Fig. 4 is avertical sectional view of a modified metalfeeding device.

Ph0t0micrographs.Fig. 5 is a photomicrograph, magnification diameters,of the metal structure at the center of a 12" x 12" aluminum alloy ingotas cast by. the method described in the aforementioned Stay andHolzhauer Patent No. 1,777,657, granted October 7, 1930. Fig. 6 is aphotomicrograph, magnification 100 diameters, of the metal structure atthe center of a 12" x 12" ingot of the same aluminum alloy as thatrepresented in Fig. 5 as cast by the method of the present invention.Fig. 7 is a photomicrograph, magnification 100 diameters, showing, inlongitudinal section, the metal structure at the center of a 6" x 6"bloom as rolled from the ingot of Fig. 5. Fig. 8 is a photomicrograph,magnification 100 diameters, showing, in longitudinal section, the metalstructure at the center of a 6" x 6" bloom as rolled from the ingot ofFig. 6.

Graphs-Fig. 9 is a graphical representation of essential steps of thegeneral method.

Reference will first be had to Figs, 1 m4, inclusive, illustrating anembodiment of the apparatus for carrying out the method. Figs. 1 and 2show a general arrangement of such apparatus, in which a main framestructure I supports a mold shell 2 conveniently located above a castingpit 3. A portion of the main frame structure I consists of a columnextending down into the casting pit 3, which column, in the structureshown, takes the form of I-beams 4, 4. The I-beams 4, 4 serve as avertical runway or track for the carriage 5 which is provided with twopairs of flanged wheels 6, 6 and I, 1 bearing against the flanges ofI-beams 4, 4 on opposite sides thereof. The carriage 5 carries ahorizontal platform 8 and supporting structure therefor, which platformforms the bottom of the mold.

Metal is fed into the mold from an electric pouring ladle 9 through thepouring spout l0, adjustable trough II, and cooperating vertical feedingmean I2.

The carriage 5 with the mold bottom 8 is arranged for vertical movementwhich, in the apparatus illustrated, is accomplished by means of cableand winch. A- cable l3 passes over fixed pulleys l4 and I5 mounted inthe column formed by the Lbeams 4, 4 and over a movable pulley I6mounted in the carriage 5, and is secured adjacent the fixed pulley 15.Cable I3 is wound over a drum I! supported in the main frame I. Thiswinding drum I1 is driven by a variablespeed motor l8 acting through thepinion l9 and gear wheel 20, which latter is keyed to the same shaft asthe winding drum H.

The lowering rate of the carriage 5 may be controlled by any well knownmeans, as by the variable-speed motor I 8 here shown, the speed of whichcan be controlled from the operating platform by means of the hand wheel2| acting through the control shaft 22.

Means are provided for cooling the mold shell 2 and also for directlychilling the embryo ingot as it is lowered below the plane of the bottomedge of the mold shell. This cooling is preferably accomplished by meansof a water spray directed around the periphery of the mold shell bymeans of spray pipes 23 and 24, the water jets or spray from which actrespectively against the outer surface of the mold shell 2 and thesurface of the embryo ingot as it emerges there below. I prefer alsothat the mold bottom 8 be cooled as by means of water delivered into thecooling chamber 25 through a pipe and flexible hose connection 26.

- tube at 41.

The metal feeding means is shown to a larger scale in Fig. 3, in whichthe mold bottom 8 has been lowered so that the embryo ingot 21 is seenemerging from the bottom of the mold shell 2. The pouring trough II isvertically adjustable at the ladle end by any suitable means 28 (seealso Fig. 1) so as to bring it into the proper position to receive themolten metal from the pouring spout III of the ladle. The other end ofthe pouring trough ll likewise is provided with a vertical adjustment asby the rack 29 and pinion 38 with its operating crank 3i, the pouringtrough H being pivotally supported on the lower end of the rack 29 as at32. Extending below the pouring trough H is a vertical standpipe 33 incommunication with the trough at its upper end, and at its lower endbeing opento the mold. Opposite the lower end of standpipe 33 is ahorizontal baflle plate 34 supported on rods 35 which pass throughprojections 36 on either side of trough ll. These rods 35 are threadedin the projections 38 to provide a vertical adjustment for the baffleplate 34 by tumlng the handles 38 on the rods 35. This adjustment isused to vary the opening between the bottom of standpipe 33 and thebaiiie plate, thereby to control the rate of discharge of the moltenmetal from the lower end of the metal feeding means. I have found itdesirable to employ a skimmer 39, consisting of a vertical ballle platearranged to form an enclosure around the feeding device at the level ofthe metal in the mold. This skimmer 39 may be provided with a verticaladjustment similar to that used for the pouring trough II and consistingof a rack 48 and pinion 4| operated by a crank 42.

It will be noted that the various adjustments described in connectionwith the pouring trough II and skimmer 39 provide for introduction of"the metal without turbulence at various levels within the mold shell 2,thus permitting the maintenance of any desired head of metal in themold, the term head being used here to indicate the depth of themetal inthe mold shell 2, i. e., the distance from the plane of the lower edgeof the mold shell to the surface of the molten metal. This arrangementlikewise makes it possible to lift the pouring trough and standpipeassembly, ll, 33 out of the mold, and

when the skimmer 39 is raised to an extent permitted by the rack andpinion 48, 4|, the rack support 43 which is hinged to the main frame Iat 44 can be tilted back out of the way at the end of the ingot castingoperation.

A modified form of metal feeding device is shown in Fig. 4 in verticalcross section, looking toward the ladle. Here the pouring trough isrepresented at 46, and the standpipe or pouring In this form, thestandpipe is restricted at its lower end to form the orifice 48. Theflow of the metal through the orifice 48 is controlled by the rod 49which acts as a valve, being raised or lowered by turning the handle 50to operate its screw-threaded engagement with the rod support Below theorifice 48 is a horizontal baffle plate 52 which in this case is notadjustable with respect to the standpipe or pouring tube. This modifiedform of metal feeding arrangement may be used in coniunction with theskimmer, mold and other parts illustrated in Fig. 3.

In the preferred practice of my invention, the inner walls of the moldshell 2 are provided with a layer of solid lubricant, preferably grease.

Under some conditions of operation, it may be produces marked advantagesover a liquid.

found that a wax or other non-metallic substance serving to space themolten metal from the walls of the mold shell may be used with goodresults. I have found in particular that a solid lubricant It need notbe renewed at any time during the casting of even the largest andlongest ingot, due to my surprising discovery that, even under the action. of the molten metal which is continuously cast into the moldagainst the layer of lubricant and drawn past it, a very appreciableamount of the lubricant remains in place on the mold wallsin fact, anamount readily visible to the naked eye and which can be rubbed off withthe finger. In operation, the mold bottom 8 is brought up into theposition which it ocupies in Figs. 1 and 2, and the metal feeding meansll, 33 and skimmer 39 lowered into the mold 2, as shown in thesefigures. Wire clips 45 may be inserted in the mold bottom (see Fig. 3),these clips being bent underneath the mold bottom 8 and also beinghooked over at their upper ends in such a way that the first metal castin the mold, when solidified around the clips 45, is fastened to themold bottom 8. This insures that, at the beginning of the castingoperation when the mold bottom first begins to move downwardly, theembryo ingot will likewise start to move downwardly. Once the operationis well under way, the weight of the cast metal insures its continuoustravel down through the mold. Now with the parts in the positiondescribed, the electric pouring ladle 9 is tilted by means of any of themechanisms well known for this purpose (not shown) so that the moltenmetal flows into the trough II and down through the standpipe 33 againstthe horizontal baffle plate 34 and laterally outwardly toward the moldshell 2 underneath the lower edge of the skimmer 39. As the metalreaches the bottom and edges of the mold, it is cooled by the water inthe chamber 25 and the water spray 23, beginning to solidify around theperiphery. As soon as the metal in the mold has built up to the desiredhead, as determined in accordance with the size and shape of the crosssection of the ingot, the rate of lowering of the metal through themold, and character of the particular alloy being cast, the motor I8 isstarted in order to lower the carriage 5 and mold bottom 8 at thepredetermined rate. For aluminum alloys of the type now in usecommercially in the production of the large structural shapes andforgings from the ingot produced by my method, I have found it isadvantageous to employ lowering speeds of between 1 and '7 inches perminute. lifter the lowering speed and thickness of metal head within themold have been selected, the horizontal baffle plate 34 and level of themolten metal in the trough II are adjusted to maintain these conditionsin equilibrium during the entire casting operation. As the embryo ingotpasses out of the mold and below the plane of the lower edge thereof, itis chilled directly by the water spray from the pipe 24. This sprayimpinges against the surface of the embryo ingot on all sides and runsdown the sides thereof. Ingot of any desired length may be produced inthis manner, and'the operation is terminated at the desired moment byinterrupting the fiow of metal into the mold, whereupon the completedingot is withdrawn entirely below the mold and removed from the castingpit. A completed ingot is indicated by the dot dash lines 53 in Fig. 1.

In this specification, the term embryo ingot is used to refer to theingot in the process of formation, and includes all of the metal belowthe upper liquid surface down to the point where the lowest freezingeutectic of the metal is entirely solidified. Effective area of the moldwalls is used with reference to that portion of the inner surface of themold shell 2 which lies between the plane of the upper liquid surface ofthe metal in the mold (for a given head) and the plane of the lower edgeof the mold shell.

Attention is directed to the fact that the head of metal in the mold isrelatively small in comparison with the size of the ingots crosssection. This is of importance in producing a light metal andparticularly an aluminum or aluminum alloy ingot possessing thedesirable characteristics outlined in the statement of object. Anotherfactor of importance is the rapid rate of lowering of the embryo ingotthrough the mold shell. These factors, together with the rate ofapplication of the liquid coolant directly to the surface of the embryoingot as it emerges below the mold shell, govern the temperaturegradient within the embryo ingot, and therefore the rate at which heatis abstracted in cooling the metal to below its solidus or below thetemperature at which the lowest freezing eutectic has entirelysolidified. These factors also determine what portion of the total heatcontent of the ingot above room temperature is withdrawn through themold walls, or which is withdrawn from that portion of the embryo ingotwhich lies above the plane of the bottom edge of the mold shell.

It is, of course, obvious that the factors under discussion must bevaried in accordance with the shape of the cross section of the ingot,whether it is a solid or a hollow ingot, or whether it is round, squareor rectangular. In general, a common denominator is provided by theminimum transverse dimension of the ingot cross section; for it is thisdimension which largely determines the proper distance between themolten metal and the point of direct application of the liquid coolantto the surface of the embryo ingot.

It will be recalled that one of the stated objects of the invention isto provide an ingot casting method by which sound aluminum ingot may beproduced, which ingot is particularly characterized by the fineness andevenness of distribution of its alloying constituent, with especialreference to the network of the undissolved constituent. This object maybest be explained with reference to Figs. 5 to 8, inclusive, of thedrawings which will now be described in greater particularity. Fig. 5 isa photomicrograph, magnification 100 diameters, of the metal structureat the center of a 12" x 12" aluminum alloy ingot as cast by the methoddescribed in the aforementioned Stay and Holzhauer Patent No. 1,777,657,granted October 7, 1930. The alloy is one of the common strong aluminumalloys much in use today, containing about 4.0 per cent of Cu, about 0.5per cent Mn, and about 0.5 per cent Mg. The cell area, constituentparticle size, and particularly the dendritic segregation of insolubleconstituent should be noted for purposes of comparison with Fig. 6 whichis a photomicrograph, magnification 100 diameters, of the metalstructure at the center of a 12" x 12" ingot of the same aluminum alloyas that represented in Fig. 5 as cast by the method of the presentinvention. The points to be noted in comparing Fig. 6 with Fig. 5 are:smaller cell areas, greater unlformity of distribution of constituents,smaller particle size of constituents (also evident from the increase inthe number of particles present),

and the strikingly lesser extent of dendritic segregation of insolubleconstituents. Two such corresponding areas are indicated by circles inFigs. 5 and 6.

Fig. 7 shows the metal structure at the center of a 6" x 6" bloom asrolled from the ingot represented in Fig. 5; and Fig. 8 shows the metalstructure at the center of a 6" x 6" bloom as rolled from the ingotrepresented in Fig. 6. Both of these photomicrographs are at themagnification of diameters and are longitudinal sections. Refinement ofthe constituent particle size and the uniformity of distribution thereofin the bloom rolled from ingot produced in accordance with my method,for instance as in Fig. 8, is characteristic, and will be seen to be farsuperior to that produced in a bloom rolled from the same alloy as castby the best method known to the art prior to the present invention (Fig.7). Of particular importance is a marked decrease in the extent ofdendritic segregation of insoluble constituent in the structure of Fig.8. The areas of dendritic segregation are represented by the darkparticles in Fig. 7, but these areas are difficult to distinguish inFig. 8 by reason of their small size.

I have found that, by holding within certain limits the percentage ofthe total heat content of the metal which is abstracted at the mold, therate of such abstraction of heat, and the rate of abstraction of heatfrom the embryo ingot immediately below the plane of the bottom edge ofthe mold down to the point where the lowest freezing eutectic isentirely solidified, it is possible to produce, as cast in ingot of verylarge cross section, a metal such as represented in Fig. 6, and which ischaracterized by a structure in which the undissolved constituent isuniformly distributed in finely divided form; which possesses, to anextent heretofore unattained in ingot of large cross section, thedesirable working characteristics visibly represented in Fig. 8 (75 percent reduction by rolling); and which is remarkably free from crackingduring severe working operations leading to the production of finishedwrought and heat-treated articles of superior mechanical properties,examples of which will be given hereinbelow.

The limits within which the rate of heat abstraction from that portionof the embryo ingot which lies above the plane of the bottom of the moldshell and that which lies immediately below such plane must bemaintained, in order to obtain the advantages of the present invention,may best be explained with reference to the diagrammatic representationof Fig. 9. In the graph of Fig. 9, I have plotted, as abscissae, elapsedtime in seconds and, as ordinates, the averag heat content (above roomtemperature) of a transverse section through the embryo ingot one inchin length as expressed in B. t. u. per cubic inch. A scale ancillary tothe abscissa scale of elapsed time is provided to show the distance ofthe section considered below the liquid surface in inches for any givenelapsed time.

Curves plotted to these coordinates show the falling oil in heat contentof the metal as it passes down through the mold and past the point atwhich the lowest freezing eutectic solidifies. The diagram at the top ofFig. 9 is plotted against the same elapsed time and distance scales asform the abscissa for the graph. Consider a section whose length L isone inch (length being used herein to refer to dimensions parallel tothe longitudinal axis of the ingot), as it passes down through the moldfrom the upper liquid surface to the plane of the lower edge of the moldshell 2 and on past this plane to a point beyond which the lowestfreezing eutectic has solidified. According to my invention, this lastpoint will never lie appreciably beyond a distance equal to one-half theminimum transverse dimension of the ingot section. That portion of theembryo ingot which lies above the plane of the bottom edge of the moldshell 2 is represented by the dimension a, and that portion which liesimmediately below the plane of the bottom edge of the mold and which isof a length equal to one-half the minimum transverse dimension of theingot section is represented by the dimension D. The rate of cooling ofthe embryo ingot over the time and distance a+b is of criticalsignificance in achieving the objects and results of my invention.Within limits depending primarily upon the shape of the ingot crosssection, and upon other considerations such as the composition of thealloy, the dimension d (regarded either as time or distance) isvariable; and dimension 1), by definition, varies according to theminimum transverse dimension of the ingot section. However, within thelimits of variation of a and b, the rate at which heat is withdrawn inorder to produce my improved ingot structure is illustrated in thegraph.

The curve 54 over an elapsed time of 250 seconds, which may berepresented as 54am, depicts the rate of loss in average heat content ofa transverse section one inch in length for an ingot, exemplified by themicrostructure of Fig. 6, as cast by my improved method. In the diagramat the top of Fig. 9, this typical ingot is represented in the processof formation, isotherms being plotted along the central vertical crosssection thereof for temperatures of 1185 degrees F., 960 degrees F., 800degrees F., 600 degrees F., 400 degrees F., and 200 degrees F. Above1185 degrees F., the alloy may be considered to be in the liquid state.For the ingot represented, the average temperature of the metal asintroduced at the liquid surface of the metal in the mold was 1214degrees F. The ingot represented was 12"x12" in cross section and wascast of an aluminum alloy containing about 4.0 per cent Cu, 0.5 per centMn and 0.5 per cent Mg. After I had discovered the critical coolingrates within which the improved metal structure could be obtained,careful calorimetric measurements were made in order that. a betterunderstanding of the theory of the invention might be obtained. A watertrough was constructed around the outside of the lower edge of the moldshell 2 in order that the quantity and final temperature of the waterused to cool the mold shell might be determined, and an accurate figurebe obtained for the amount of heat abstracted through the mold shell 2.Thermocouples were arranged in the mold in such a way as to traveldownwardly therethrough with the embryo ingot during the castingprocess, providing the data from which were plotted the isotherms shownin th diagram.

The curve 54m, takes into account the latent heat of fusion of themetal, and, by its slope, indicates the change in rate of heatabstraction as a unit of length of the metal passes downwardly throughthe mold over the distance a b. It is to be noted that a definite thoughrelatively small portion of the heat is removed over the time anddistance a, and that the average rate of heat abstraction over thedistance D is greater than that over the distance a, as shown by theincrease in average slope of curve 54b over curve 54.. I have foundthat, in order to produce the improved metal structure typified by thatof an ingot cooled at the rate represented by the curve 5a,b, it isnecessary to cool the mold shell while simultaneously applying a liquidcoolant directly and rapidly to the metal below the mold shell at a rateadjusted to withdraw from that portion of the embryo ingot which liesabove the plane of the bottom edge of the mold shell at least 2 B. t. u.per minute per cubic inch average per inch of length averaged over thelength of said portion and to withdraw from that portion of the embryoingot which lies immediately below the plane of the bottom dge of themold shell at least 6 B. t. u. per minute per cubic inch average perinch of length averaged over the length b which is equal to one-half theminimum transverse dimension of the ingot section. Curve 551,11,provides a graphical representation of these limits. In some cases, forexample, with alloys of the type described hereinabove, I have found itpreferable to withdraw from that portion of the embryo ingot which liesimmediately below the plane of the bottom edge of the mold shell atleast 10 B. t. u. per minute per cubic inch average per inch of lengthaveraged over the length b. Curve 56a,b, provides a graphicalrepresentation of this preferred limit when combined with the limit of-2 B t. u. per minute per cubic inch average per inch of length for therate of withdrawal of heat from that portion of the embryo ingot whichlies above the plane of the bottom edge of the mold shell. Curves 55 and56 coincide over the time and distance a. Curve 51 is not critical withrespect to the attainment of the objects of the present invention andmay vary according to the size and shape of the ingot cross section. Itwill be understood that there is alimit beyond which the slope of thecurve 51 cannot practicably be increased, and the curve 511: has beenshown merely to indicate what I consider as, in general, a practicableminimum cooling rate over the distance I).

The shaded area between the curves 553,1, and 511 represents the coolingrates at the mold and below the mold within which the advantages of myinvention may be attained for the ingot shown, and I consider that thelimiting conditions represented by curve 55.13: are critical.

I have found further that, in order to produce the best results, notmore than between 7 and 25 per cent of the total heat content of themetal above room temperature should be withdrawn through the mold shell,and that if the cooling rate is adjusted to within these limits and aliquid coolant is applied directly and rapidly to the metal below themold shell to withdraw the balance of the total heat content, a metalstructure such as that illustrated in Fig. 6 can readily be obtained.

One of the novel features of my method resides in carrying a shallowmetal head within the mold shell, that is, looking at Fig. 9, thedimension a is quite shallow with respect to the cross sectionaldimensions of the ingot. This makes it possible to apply the liquidcoolant from the spray pipe 24 directly to the surface of the embryoingot at points not farther removed from the level of the surface of themolten metal in the mold than twice the minimum transverse dimension ofthe ingot, thus to produce a sharp temperature gradient in cooling themetal to below the solidus. The cooling rate over the distance a isdetermined, in part, by the heat withdrawn through the mold shell 2,and, in part by the heat withdrawn by the direct application of theliquid coolant from the spray pipe 24 below the lower edge of the moldshell 2. It is to be noted that the rate of cooling through the shelland the rate of cooling below the shell may bear such a relation to eachother as to produce irregularities in the shape of the isotherms. Insome cases this effect may be observed as indicated at 58 in Fig. 9 andthe observations which I have made appear to indicate such amanifestation.

When other conditions heretofore defined have been satisfied byadjusting the rate at which molten metal is introduced into the moldshell 2 and the rate at which the metal is lowered through the mold aswell as the points at which the liquid coolant is applied directly tothe metal through the spray pipe 24, its temperature and quantity, asharp temperature gradient will be maintained from the center of theingot to the sides thereof. More specifically, it will be found thatfrom all points on the ingot surface in a horizontal plane just belowthe bottom of the mold shell, the mean minimum distance to the moltenmetal will be maintained at not greater than one-half of the smallesttransverse dimension of the ingot. The metal at the ingot center willstill be molten in the horizontal plane at which the liquid coolant isapplied directly to the ingot surface but should not be molten at agreater distance below the plane of the bottom of the mold shell thanthe minimum transverse dimension of the ingot. Conversely, when theseconditions are satisfied by making the named adjustments, the conditionsotherwise defined will have been satisfied, and the principal objects ofmy invention realized.

It is quite essential to the successful practice of my invention thatthe molten aluminum be introduced into the mold shell in a manner toproduce quiet, radially outward flow of the metal toward the mold shellnear the top surface of the metal in the mold. The apparatus foraccomplishing this has been described with reference to Figs. 3 and 4 ofthe drawings, in which the horizontal bafiie means 34 or 52 areutilized. The metal as it reaches the surface of the metal in the moldis directed outwardly in all directions toward the mold shell 2 where itis cooled principally by the abstraction of radiant energy withoutmetal-to-metal contact between the introduced metal and the mold walls,whereby a controlled and relatively small amount of the total heatcontent of the metal is withdrawn through the mold. The horizontalbaflle means restricts the downward flow of the metal entering the mold.In the preferred practice of my method, the temperature of the moldwalls at the level of the metal surface in the mold is maintained below200 degrees Fahrenheit.

Reference has already been made to the maintenance of a relativelyshallow head a of metal in the mold shell 2. This feature of the methodis perhaps best defined with reference to the apparatus employed. Inorder that a relatively small and controlled amount of heat beabstracted from the metal at the mold, that is, above the plane of thelower edge of the shell 2, it is necessary that the effective area ofthe mold walls be restricted according to the cross sectional area ofthe ingot. I have found that the effective area of the mold walls shouldnot be more than three times the cross sectional area of theingotpreferably from one to three times its cross sectional area. Formost ingot sizes, the lowering speeds will vary between 1 and 6 inchesper minute.

I shall now describe a specific example of the practice of my invention.A 12" x 12" bronze mold shell such as illustrated in the drawings wasprepared by coating its interior walls with a film of heavy grease. Themold bottom was raised into the position shown in Figs. 1 and 2, thmetal feeding means, skimmer, and horizontal baiile means lowered intoposition in the mold shell, and the cooling water turned on in the spraypipes 23, 24, and in the flexible hose connection 28 feeding the coolingchamber 25. The electric pouring ladle 9 was then tilted to feed metalinto the pouring trough II and downwardly through the vertical feedingmeans I2. As soon as the head of metal had built up to 4 inches abovethe plane of the lower edge of the mold shell 2, the motor 18 wasstarted and the hand wheel 2| adjusted to lower the carriage 5 and themold bottom 8 at a speed maintained at about 2.4 inches per minute. Themetal was an aluminum alloy comprising 4.0 per cent Cu, 0.5 per cent Mn,and 0.5 per cent Mg, balance substantially aluminum plus impurities, andwas maintained at a temperature averaging 1214 degrees Fahrenheit at thesurface of the molten metal in the center of the mold. The rate ofapplication of the cooling water was adjusted to withdraw from thatportion of the embryo ingot which lay above the plane of the bottom edgeof the mold shell 6.5 B. t. u. per minute per cubic inch average and towithdraw from that portion of the embryo ingot represented at b in Fig.9, 11 B. t. u. per minute per cubic inch average. When the ingot hadreached a length of 8 feet, the metal feeding was discontinued, theingot cooled and removed. The ingot was then heat-treated at 930 degreesFahrenheit for 6 hours and quenched in water. Test samples taken fromingot so produced were subjected to tensile tests with the followingaverage results:

These properties are superior to those obtained by the best practiceknown prior to my invention, which, for ingot of the same size and alloycomposition, shows elongations on the order of 2.8 to 3.5 per cent infour diameters and tensile strengths on the order of 35,800 to 39,100.Although the values obtained by the best prior methods may sometimes begreater than this, no consistency is to be expected at figures greaterthan those given. The ingot as produced by the method just outlined wasfree from objectionable cracking, its metal structure characterized bythe fineness and evenness of distribution of its alloying constituent,and large wrought and heat treated articles made therefrom possessedimproved mechanical properties. Most of the stock rolled from largeingot produced in accordance with my method gives very high values intransverse tests, such values as 55,000 pounds per square inch tensilestrength with 15 to 18 per cent elongation being common.

While I have described my invention particularly with reference toaluminum, it is applicable also to magnesium and its alloys and thusbroadly relates to the common light metals and light metal alloys. Theprinciples specifically described hereinabove with reference to one ofthese light metals--aluminum--may also be used with success in thecasting of the other light metal--magnesium. For example, it has beenfound that a magnesium base alloy composed of magnesium and about 1.5per cent manganese can be successfully cast in the form of a 7" x 16''ingot from which very satisfactory sheet can be rolled. This wasaccomplished by heating the alloy to a pouring temperature of about 1400F., transferring it to the mold shell in the manner describedhereinabove. A 3 inch head of metal was maintained in the mold and theingot lowered at a rate of about 4 inches per minute. The mold shell waslubricated in the same manner as was done in casting aluminum alloyingots, and the water sprays were likewise adjusted to deliver about thesame volume of water as was used in making aluminum alloy ingots of thesame size. rolled to sheet form without dimculty, the sheets being of aquality equal to, or better than, sheets obtained from ingots castaccording to older' methods.

My method and apparatus are useful in the casting of hollow ingot aswell as for casting the solid form specifically shown and, described. Inthe case of hollow ingot the liquid coolant may be applied to theinterior as well as the exterior surfaces of both the mold shell and theingot. I intend to cover all such modifications of the inventiondescribed as fall within the purview of the claims.

This application is a continuation-in-part of my application for UnitedStates patent flied October 14, 1936, Serial No. 105,631.

I claim:

1. In the casting 'of ingots of light metals and alloys thereof bycontinuously pouring metal into a downwardly open mold shell andwithdrawing part of the heat from the metal through the shell and partof the heat through the metal below the shell, the improvementcomprising forming and moving downwardly in the shell an embryo.ingot,adjusting and maintaining the withdrawal of heat through the shell andbelow the same to provide a sharp temperature gradient between the sidesof the ingot and the freezing metal as exemplified by the fact that themolten metal does not extend below the plane of emergence to a distancegreater than the minimum transverse dimension of the ingot, andadjusting and maintaining the pouring rate and the rate of withdrawal ofthe ingot from the shell to maintain the upper surface of the moltenmetal close to the plane of emergence of the embryo ingot from theshell.

2. In the casting of ingots of light metals and alloys thereof bycontinuously pouring metal into a downwardly open mold shell andwithdrawing part of the heat from the metal through the shell and partof the heat through the metal below the shell, the improvementcomprising forming and moving downwardly in the shell an embryo ingot,adjusting and maintaining the withdrawal of heat through the shell andbelow the same to provide a sharp temperature gradient between the sidesof the ingot and the freezing metal, and adjusting and maintaining thepouring rate and the rate of withdrawal of the ingot from the shell sothat the effective area of the mold wall will not be more than threetimes the cross-sectional area of the ingot.

3. In the casting of ingots of light metals and The ingot was i alloysthereof by continuously pouring metal into a downwardly open mold shelland withdrawing part of the heat from the metal through the shell andpart of the heat through the metal below the shell, the improvementcomprising forming and moving downwardly in the shell an embryo ingot,adjusting and maintaining the pouring rate and the rate of withdrawal ofthe ingot from the shell and the withdrawal of heat through the shelland below the same, so that from all points on the outside surface ofthe ingot which lie in the plane of emergence of the ingot from theshell the mean distance to molten metal will be not greater thanone-half the smallest transverse dimension of the ingot, and so thatmetal at the ingot center will still be molten in the plane of emergenceof the ingot but will not be molten at a greater distance below saidplane than the minimum transverse dimension of the ingot.

4. In the casting of ingots of light metals and alloys thereof bycontinuously pouring metal into a downwardly open mold shell andwithdrawing part of the heat from the metal through the shell andv partof the heat through the metal below theishell, the improvementcomprising forming andlmoving downwardly in and through the shell anembryo ingot, adjusting and maintaining the pouring rate and the rate ofwithdrawal of the ingot from the shell, and the withdrawal of heatthrough the shell and below the same, so that from all points on theoutside surface of the ingot which lie in the plane of emergence of theingot from the shell the mean distance to molten metal will be notgreater than one-half the smallest transverse dimension of the ingot,and so that the total depth of molten metal above the lowest point ofunsolidifled metal is less than the minimum transverse dimension of theingot.

5. In the casting of ingots of light metals and alloys thereof bycontinuously pouring metal into a downwardly open mold shell andwithdrawing part of the heat from the metal through the shell and partof the heat through the metal below the shell, the improvementcomprising forming and moving downwardly in the shell an embryo ingot,adjusting and maintaining the pouring rate and the rate of withdrawal ofthe ingot from the shell and the withdrawal of heat through the shelland below the same, so that metal at the ingot center will still bemolten 'in the plane of emergence of the ingot but will not be molten ata greater distance below said plane than the minimum transversedimension of the ingot.

6. In the casting of ingots of light metals and alloys thereof bycontinuously pouring metal into a downwardly open mold shell andwithdrawing part of the heat from the metal through the shell and partof the heat through the metal below the shell, the improvementcomprising forming and moving downwardly in the shell an embryo ingot,adjusting and maintaining the withdrawal of heat through the shell andbelow the same to provide a sharp temperature gradient between the sidesof the ingot and the freezing metal, and adjusting and maintaining thepouring rate and the rate of withdrawal of the ingot from the shell tomaintain the upper surface of the molten metal close to the plane ofemergence of the embryo ingot from the shell, and so that from allpoints on the outside surface of the ingot which lie in the plane ofemergence of the ingot from the shell the mean distance to molten metalwill be not greater than one-half the smallest transverse dimension ofthe ingot, and so that metal at the ingot center will not be molten at agreater distance below said plane of emergence than the minimumtransverse dimension of the ingot.

7. In the casting of ingots of light metals and alloys thereof bycontinuously pouring metal into a downwardly open mold shell andwithdrawing part of the heat from the metal through the shell and partof the heat through the metal below the shell, the improvementcomprising forming and moving downwardly in the shell an embryo ingot,adjusting and maintaining the withdrawal of heat through the shell andbelow the same to provide a sharp temperature gradient between the sidesof the ingot and the freezing metal, and adjusting and maintaining thepouring rate and the rate of withdrawal of the ingot from the shell tomaintain the upper surface of the molten metal close to the plane ofemergence of the embryo ingot from the shell, so that metal at the ingotcenter will not be molten at a greater distance below the plane ofemergence of the ingot from the shell than the minimum transversedimension of the ingot.

8. In the casting of ingots of light metals and alloys thereof bycontinuously pouring metal into a downwardly open mold shell andwithdrawing part of the heat from the metal through the shell and partof the heat through the metal below the shell, the improvementcomprising forming and moving downwardly in the shell an embryo ingot,and adjusting and maintaining the withdrawal of heat through the shelland below the same so that between about 7 and 25 per cent of the totalheat content of the metal above room temperature is continuouslywithdrawn through the shell, thereby to produce a sharp temperaturegradient between the sides of the ingot and the freezing metal.

9. In the casting of ingots of light metals and alloys thereof bycontinuously pouring metal into a downwardly open mold shell andwithdrawing part of the heat from the metal through the shell and partof the heat through the metal below the shell, the improvementcomprising forming and moving downwardly in the shell an embryo ingot,and adjusting and maintaining the withdrawal of heat through the shelland below the same so that between about 7 and 25 per cent of the totalheat content of the metal above room temperature is continuouslywithdrawn through the shell, thereby to produce a sharp temperaturegradient between the sides of the ingot and the freezing metal, andadjusting and maintaining the pouring rate and the rate of withdrawal ofthe embryo ingot from the shell to maintain the upper surface of themolten metal close to the plane of emergence of the ingot from theshell.

10. In the casting of ingots of light metals and alloys thereof bycontinuously pouring metal into a downwardly open mold shell andwithdrawing part of the heat from the metal through the shell and partof the heat through the metal below the shell, the improvementcomprising forming and moving downwardly in the shell an embryo ingot,while adjusting and maintaining the pouring rate and the rate ofwithdrawal of the embryo ingot from the shell to maintain a metal headwithin the shell which is shallow with re-- spect to the cross-sectionaldimensions of said ingot, and to provide that the molten metal does notextend below the plane of emergence to a distance greater than theminimum transverse dimension of the inset.

11. The process of solidifying molten metal into ingot which comprisescontinuously supplying molten metal to a vertically disposed mold andcontinuously withdrawing metal from said mold while maintaining only asmall amount of molten metal in said mold as evidenced by the fact thatthe total depth of molten metal above the lowest point of unsolidifledmetal is less than the minimum transverse dimension of the ingot.

12. The process of casting light metals and a1- loys thereof whichcomprises continuously supplying molten metal to a vertically disposedmold, continously withdrawing metal from said mold, and maintaining theupper surface of molten metal in said mold close to the plane ofemergence of the ingot from said mold as evidenced by the fact that thelowest point of unsolidified metal lies below the plane of emergence ata distance no greater from the said upper surface of molten metal thanthe minimum transverse dimension of the ingot.

13. In the method of continuous casting of metal in a thin molding tubeof high thermal conductivity cooled by a flowing thin sheet of fluid incontact with the outer walls of the tube, the step of maintaining on theinner wall of the tube a film of lubricating material having a meltingpoint substantially lower than that of the metal being cast.

14. In the process of solidifying molten metal into ingot whichcomprises continuously supplying molten metal to a mold shell, the endsof which are open, and withdrawing at least a part of the heat from themetal through said shell, the improvement comprising adjusting andmaintaining the withdrawal of heat and the rate of withdrawal of themetal from the shell so that the distance, as measured along the centerline of the body of metal in the direction of its travel, between aplane perpendicular to the said direction of travel and containing thepoint at which solidificatoin of metal first begins and a planeperpendicular to the said direction of travel and containing the pointat which all solidification is first completed shall not be greater thanthe minimum transverse dimension of the ingot.

WILLIAM T. ENNOR.

I CERTIFICATE OF CORRECTION. Patent 2,501,027. November 5, 19u2.

WILLIAM 1r. ENNOR.

It is hereby \certified that error appears in the printed specificationof the above numbered patent requiring correction as follows: Page 5,sec- 0nd column, line 16, for "ocupies" read --occupies--; page 5,second column, line 14.5, for "minimum" read --maximum--; page 8, secondcolumn, line 6, claim 11+, for "solidificatoin" read -solidification--;and that the said Letters Patent should be read with this correctionthereinthat the same may conform to the recor d of the case in the.Patent Office.

Signed and sealed this 8th day. of December, A. D. 19h2.

vHenry VanArsda-le, (Seal) Acting \Commissioner of Patents.

